I'm installing an outdoor power center/transfer switch next to my meter. The service is 200Amps and currently they used 4/0 Al to run from the meter to the main breaker. I'm going to re-wire with 2/0 Cu from the meter to the power center and then also run 2/0 Cu back from the power center/transfer switch to the Main Braker. What else do I need to do here with the Neutrals and Grounds to maintain code?

The power center has the ability to add branch breakers and I'm going to have a 100 branch breaker feeding underground through PVC to a detached garage abour 40 feet away. What size Cu wire will be best for this installlation and how do the Neutrals and grounds need to be handled for that?

My fist question would be how are you doing this with the power on? Are you having the power company shut down power while you work?

We're going to pull the meter during the work. No way I'm doing this live. I'd rather avoid having the utility shut off at the transformer. Still need to be careful of the line side of the meter but we'll cover those terminals and be careful of them. I've discussed installation with the county inspector and he's OK with the plan. I'm just wanting to be clear on wire sizes and the possibility of derating neutrals and ground wires to save cost. It seems that Service Entrance cable ampacity ratings are different than branch cable ampacity ratings.

I'm assuming the power center neutral gets bonded to the ground as it is now the service entrance equipment. I also assume the neutrals for the main breaker for the house and the main lug panel for the detached garage are not bonded but now have floating neutrals and separate grounds.